Projection optical system

ABSTRACT

In a 1-2nd lens group, an aspherical resin lens is disposed on the outermost enlargement side, an enlargement-side fixed lens group (second fixed lens group) as a fixed group is disposed, a moving lens group, which move when focusing is performed in response to the magnification change, is disposed further on the reduction side from the second fixed lens group. Even in a case where the second optical group is configured of one mirror, it is possible for a primary image to have appropriate aberration and to hereby reduce aberration of an image which is finally projected onto a screen through the second optical group.

BACKGROUND

1. Technical Field

The present invention relates to a projection optical system suitablefor being incorporated in a projector which performs enlargementprojection of an image of an image display element.

2. Related Art

A refraction optical system configured to include a plurality of lensesas a projection optical system for a projector which can performprojection from a short distance and can obtain a large picture plane byhaving a wide angle of view substantially equal to a half angle of viewof 60 degrees, is proposed (see JP-A-2007-147970). However, in a casewhere a significantly wide angle of view is obtained by the refractionoptical system configured only of the lenses, there are drawbacks inthat, particularly, a lens disposed on the enlargement side is likely tobe enormously increased in side. In addition, when the refractionoptical system performs projection at a wide angle of view, it isconsidered that a large number of lenses are needed in order to correctchromatic aberration of magnification occurring by a negative meniscuslens which is positioned on the enlargement side and has great power.

As a method to solve the drawbacks of the refraction optical system, arefraction optical system formed of a plurality of lenses and arefraction/reflection complex optical system which uses at least onecurved reflective mirror have been proposed (for example, seeJP-A-2006-235516, JP-A-2007-079524 or the like). In therefraction/reflection complex optical system, since a reflective mirroris used as a final unit which obtains a wide angle of view, thechromatic aberration of magnification is unlikely to occur, compared tothe refraction optical system using only the lenses described above.

However, for example, in JP-A-2006-235516, a significantly wide angle ofview is obtained using the refraction optical system and a concavemirror; however, the curved mirror needs to be enormously increased insize and the entire length thereof needs to be enormously increased. Inaddition, in JP-A-2007-079524, for example, the angle of view is about60 degrees in the eighth example, a mirror size is decreased bycombining a concave mirror and a convex mirror. However, similar toJP-A-2006-235516, the entire length needs to be enormously increased. Inaddition, the F-number is about 3 and it is dark and an optical systemusing a transmissive liquid crystal is defective in terms of brightness.Moreover, two mirrors have an aspherical surface, which causes a highdegree of difficulty in terms of achieving accuracy and assembly.

As above, in the refraction/reflection complex optical system, anultra-wide angle of view is obtained but it is difficult to decrease theentire length, and thereby there are drawbacks in that the mirror isincreased in size. For example, the system is not suitable for equipmentsuch as a front projector in which portability is important.

In comparison, a system in which a reflective mirror is used as a frontprojector has been known (JP-A-2008-250296, JP-A-2012-203139, or thelike). For example, in JP-A-2008-250296, one or two aspherical lens isdisposed before an aspherical mirror, and thereby a compactconfiguration is achieved; however, in a system having brightness withthe F-number of about 1.7, a range of magnification change is narrowedto about 1.2 times. Conversely, in a system having a range ofmagnification change of about 2 times, it is dark with the F-number ofabout 1.85. In addition, in JP-A-2012-203139, a positive lens isdisposed closest to the mirror side in the refraction optical system,and thereby it is possible to miniaturize the mirror, which enables theentire optical system to be miniaturized. However, since the system isapplied only to the F-number of about 1.8, sufficient brightness is notobtained.

Incidentally, in the related art, a projector for the proximityapplication is usually used by being fixed during installment such asceiling installment or wall installment, with respect to a fixed screen.However, recently, there is a high demand that not only the projector isdisposed upright, and performs projection onto a table surface with arelatively small projection size, but also the projector moves to arelatively large room and can be applied to a large picture planeprojection. In a case of the large picture plane projection, in order toobtain sufficient contrast even in a relatively bright place, there is aneed to use a bright optical system even to a small extent.

SUMMARY

An advantage of some aspects of the invention is to provide a projectionoptical system which can cover a wide range of magnification change inan application to a short throw type projector and can be applied to animage display element having high resolution.

A projection optical system according to an aspect of the inventionincludes: in order from a reduction side, a first optical group which isformed of a plurality of lenses and has positive power; and a secondoptical group which has one reflective surface having a concaveaspherical shape. The first optical group is formed to include a 1-1stlens group having positive power, on the reduction side, and a 1-2ndlens group having weaker positive or negative power, compared to thepower of the 1-1st lens group, on the enlargement side, with the widestair interval as a boundary. The 1-2nd lens group includes anenlargement-side fixed lens group which is disposed on the outermostenlargement side, is fixed when focusing is performed in response to themagnification change (when focusing is performed during themagnification change), and is configured to include a plurality oflenses having at least one aspherical surface, and at least one movinglens group which moves in the optical axis direction when focusing isperformed in response to the magnification change. Here, in comparisonbetween power of the lenses and the lens groups, the relatively weakpower means a less value in a case where absolute values of power arecompared. In other words, for the power which the 1-2nd lens group has,the above description means that the absolute value thereof is less thanan absolute value of power which the 1-1st lens group has.

First, in this case of the configuration described above, the firstoptical group plays a role of causing an image of an object (that is, apanel section) to be formed as an image in front of a mirror of thesecond optical group and forming a primary image in order to form animage again on a screen by the mirror of the second optical group. Atthis time, since the second optical group is configured only of onemirror, it is difficult to individually correct aberration. Accordingly,in order to obtain a final image having small aberration on the screenby the second optical group, there is a need to form the primary imagecontaining aberration in the first optical group.

Further, in the ultra-wide angle projection optical system having theconfiguration described above, when the projection magnification ischanged, the aberration fluctuation is likely to increase because anangle of view is abnormally wide. Accordingly, the first optical groupneeds to form the primary image which contains aberration correspondingto the change of image forming magnification even when the image formingmagnification is changed.

In comparison, in the projection optical system according to theinvention, as described above, in the 1-2nd lens group of the firstoptical group, at least one moving lens group moves when focusing isperformed in response to the magnification change, and thereby it ispossible to form a primary image which is needed to obtain a good imageon the screen. Further, when focusing is performed in response to themagnification change, the moving lens group is positioned on theoutermost enlargement side and the enlargement-side fixed lens group asthe fixed group is disposed. In this manner, an influence due tounstability of the focusing group is decreased, and, in the applicationof the short throw type projector, it is possible to cover a wide rangeof magnification change and to be applied to an image display elementhaving high resolution.

In the refraction and reflection complex optical system having theultra-wide angle, since a light flux from the first optical group formedof the refraction optical system is reflected from the mirror of thesecond optical group and returns to the first optical group, there is aconcern that the lens (for example, lens positioned on the outermostenlargement side of the enlargement-side fixed lens group) of the firstoptical group on the second optical group side will interfere with thelight flux returning from the second optical group. Therefore, there isno need to have a circular shape but there is a need to have a partiallynotched shape. It is not possible for a frame structure which fixes thelens having notched shape to have a common cylindrical shape and it isdifficult to maintain accuracy. In the projection optical systemaccording to the invention, as described above, the lens group includingthe lens on the outermost enlargement side, which becomes the largest inthe first lens group and has an irregular structure, in which there is apossibility that it is difficult to maintain accuracy of the framestructure, belongs to the fixed group (enlargement-side fixed lensgroup), and thereby it is possible to prevent variation of performance.

Further, the enlargement-side fixed lens group is configured to includea plurality of lenses, it is possible to secure power mainly byspherical surface and to correct and distribute aberration by theaspherical surface, and it is possible to more stably maintain theperformance.

In a specific aspect of the invention, in the 1-2nd lens group, theenlargement-side fixed lens group is configured to include two negativelenses and an aspherical lens molded using a resin is disposed on theenlargement side. In this case, the corresponding two negative lenses,for example, the resin lens (lens relatively on the enlargement side)and the glass lens (lens relatively on the reduction side) are combined,and thereby the power of the resin lens is weakened. In addition, thelenses are configured such that the light flux is not incident to theresin lens at a steep angle, and it is possible to reduce an influenceof variations of a shape of the resin lens. To be more specific, first,the glass lens has sufficient negative power and the resin lens has weaknegative power, and thereby the correcting effects of aberration such asfield curvature, astigmatism, distortion, are achieved mainly by theaspherical surface. In this manner, it is possible to suppressdeterioration of performance due to variations.

In addition, since the resin-molded lens has a significant shrinkagefactor as general characteristics, compared to the glass-molded resin orthe like, it is difficult to secure accuracy of the surfaces. Inaddition, when the power becomes excessively strong, the resin-moldedlens has an increased uneven thickness ratio representing a ratio of thelens thickness in the vicinity of the optical axis and the lensthickness at the outer circumferential portion, and thus it is knownthat internal distortion occurs in a gate portion or in an outercircumferential portion, which influences on the performance. A linearexpansion coefficient, or a temperature coefficient of a refractiveindex of the resin is increased by one digit, compared to the case ofthe glass, which results in a focal position shift due to a focaldistance change according to a surrounding temperature or a temperaturechange during an operation. Accordingly, for the resin-molded lens, itis not preferable that a single body has strong power. On the otherhand, a cost of a lens having a large aperture can be relativelydecreased, and it is advantageous that the resin-molded lens can beapplied to a lens having a shape other than the circular shape,relatively simply.

In this manner, of the 1-2nd lens group, the resin lens is used for thelens having relatively large diameter, which is disposed on theoutermost enlargement side, not the circular shape as described above,but a notched shape may be used, and thus miniaturization and a low costis intended. At this time, the glass lens is disposed on the reductionside of the resin lens. In this manner, it is possible to appropriatelycontrol the light flux incident to the aspherical resin lens disposed onthe enlargement side and it is possible to reduce the influence relatedto disadvantage in a case of using the resin described above.

In another aspect of the invention, the 1-2nd lens group includes, asthe moving lens group, a plurality of lens groups which individuallymove when focusing is performed in response to the magnification change.In this case, the 1-2nd lens group is divided into the plurality ofgroups and moves when focusing is performed in response to themagnification change. In this manner, it is possible to correct, inbalance, a focal position at a position at which the image height is lowand the field curvature in the periphery at which the image height ishigh, and it is possible to form the primary image which is needed toobtain a good image on the screen even in a wide range of themagnification change.

In still another aspect of the invention, the 1-1st lens group isconfigured to have an aperture therein and two lenses of a positive lenswith a convex surface facing the enlargement side and a negativemeniscus lens with the concave surface facing the enlargement side, inthis order from the reduction side, on the enlargement side from theaperture. In this case, the two lenses as described above are disposedon the enlargement side from the aperture, and thereby it is possible tomaintain good performance even in a wide range of the magnificationchange.

The 1-1st lens group plays a role of efficiently receiving the lightflux from the object (that is, the panel) and sending the light flux tothe 1-2nd lens group as the focusing lens group. The 1-2nd lens group,as the focusing lens group, needs to play a role of forming anappropriate intermediate image even in a wide range of the magnificationchange. As described above, the lens group disposed on the enlargementside from the aperture of the 1-1st lens group is two positive andnegative lenses, particularly, the positive lens with the convex surfacefacing the enlargement side and the negative meniscus lens with theconcave surface facing the enlargement side are disposed in this orderfrom the reduction side, and thereby it is possible to define thesurface of the 1-1st lens group on the outermost enlargement side as anemission surface. The 1-1st lens group and the 1-2nd lens group as thefocusing lens group are hereby combined, then, it is possible tosuccessfully correct the field curvature and astigmatism characteristicsin the wide range of the magnification change and it is possible toobtain stable performance in order to form an appropriate intermediateimage.

In still another aspect of the invention, the 1-1st lens group has anaperture therein, includes at least two sets of cemented lenses ofpositive lenses and negative lenses disposed on the reduction side fromthe aperture, and has at least a concave aspherical surface on theenlargement side. In this case, an occurrence of chromatic aberration isprevented even in a configuration in which a small number of lenses areused, assembly variations is decreased, and it is possible to increasenumerical aperture (brighten).

The plurality of lenses disposed on the reduction side from the apertureof the 1-1st lens group play a role of efficiently receiving the lightflux from the object (that is, the panel) side. In a case where theplurality of lenses are configured of only the spherical lenses, thereis a possibility that the number of lenses needs to be increased. Whenthe number of lenses is increased, transmittance is reduced, the entirelength of the lens is increased due to the increase of the lenses, andthe configurational number of lenses needs to be set to the minimumextent.

For example, in order to cover the brightness having F-number of about1.6, at least one surface having the concave aspherical shape isdisposed on the reduction side from the aperture of the 1-1st lensgroup, thereby the brightness is secured, an occurrence of flare issuppressed, and it is possible to provide an image having high contrast.In addition, at least two sets of cemented lenses are configured to bedisposed on the reduction side from the aperture of the 1-1st lensgroup, thereby an occurrence of chromatic aberration is suppressed tothe smallest extent, and assembling properties are enhanced bycementing.

In still another aspect of the invention, the numerical aperture on theobject side is equal to or more than 0.3. In this case, it is possibleto form a sufficiently bright projection image.

In still another aspect of the invention, the reduction side issubstantially telecentric.

In still another aspect of the invention, elements configuring the firstoptical group and the second optical group all have a rotationallysymmetric system.

In still another aspect of the invention, a range of magnificationchange is equal to or greater than 1.5 times.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagram showing a schematic configuration of a projector inwhich a projection optical system of an embodiment is incorporated.

FIG. 2 is a diagram showing light fluxes and a configuration from anobject surface to a projection surface in the projection optical systemof the embodiment or Example 1.

FIG. 3 is an enlarged diagram showing a part from the object surface toa concave reflective mirror in FIG. 2.

FIG. 4 is a diagram showing a configuration of the projection opticalsystem of Example 1.

FIGS. 5A to 5C are diagrams showing aberration on a reduction side ofthe projection optical system of Example 1.

FIGS. 6A to 6E are diagrams showing lateral aberration of the projectionoptical system, which correspond to FIG. 5A.

FIGS. 7A to 7E are diagrams showing lateral aberration of the projectionoptical system, which correspond to FIG. 5B.

FIGS. 8A to 8E are diagrams showing lateral 1 aberration of theprojection optical system, which correspond to FIG. 5C.

FIG. 9 is a diagram showing a configuration of a projection opticalsystem of Example 2.

FIGS. 10A to 10C are diagrams showing aberration on a reduction side ofthe projection optical system of Example 2.

FIGS. 11A to 11E are diagrams showing lateral aberration of theprojection optical system, which correspond to FIG. 10A.

FIGS. 12A to 12E are diagrams showing lateral 1 aberration of theprojection optical system, which correspond to FIG. 10B.

FIGS. 13A to 13E are diagrams showing lateral aberration of theprojection optical system, which correspond to FIG. 10C.

FIG. 14 is a diagram showing a configuration of a projection opticalsystem of Example 3.

FIGS. 15A to 15C are diagrams showing aberration on a reduction side ofthe projection optical system of Example 3.

FIGS. 16A to 16E are diagrams showing lateral aberration of theprojection optical system, which correspond to FIG. 15A.

FIGS. 17A to 17E are diagrams showing lateral aberration of theprojection optical system, which correspond to FIG. 15B.

FIGS. 18A to 18E are diagrams showing lateral aberration of theprojection optical system, which correspond to FIG. 15C.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a projection optical system according to an embodiment ofthe invention will be described in detail with reference to thedrawings.

As illustrated in FIG. 1, a projector 2, in which the projection opticalsystem according to an embodiment of the invention is incorporated,includes an optical system section 50 which projects an image light, anda circuit device 80 which controls an operation of the optical systemsection 50.

In the optical system section 50, a light source 10 is, for example, anextra-high pressure mercury lamp, and emits light flux including an Rlight flux, a G light flux, and a B light flux. The light source 10 maybe a discharge light source, in addition to an extra-high pressuremercury lamp, or may be a solid-state light source, such as an LED or alaser. A first integrator lens 11 and a second integrator lens 12 have aplurality of lens elements arranged in an array. The first integratorlens 11 divides a light flux from the light source 10 into a pluralityof light fluxes. Each lens element of the first integrator lens 11condenses the light flux from the light source 10 in the vicinity of thelens elements of the second integrator lens 12. The lens elements of thesecond integrator lens 12 form images of the lens elements of the firstintegrator lens 11 on the liquid crystal panels 18R, 18G, and 18B incooperation with a superimposing lens 14. In this configuration, theentire display regions of the liquid crystal panels 18R, 18G, and 18Bare illuminated with a light flux from the light source 10, insubstantially uniform brightness.

A polarization conversion element 13 converts a light flux from thesecond integrator lens 12 to a predetermined linearly polarized light.The superimposing lens 14 superimposes the image of each lens element ofthe first integrator lens 11 on the display regions of the liquidcrystal panels 18R, 18G, and 18B through the second integrator lens 12.

A first dichroic mirror 15 reflects the R light flux incident from thesuperimposing lens 14 and transmits the G light flux and the B lightflux. The R light flux reflected from the first dichroic mirror 15 isincident to the liquid crystal panel 18R serving as an optical modulatorthrough a reflective mirror 16 and a field lens 17R. The liquid crystalpanel 18R modulates the R light flux in response to an image signal soas to form an R-color image.

A second dichroic mirror 21 reflects the G light flux from the firstdichroic mirror 15 and transmits the B light flux. The G light fluxreflected from the second dichroic mirror 21 is incident to the liquidcrystal panel 18G serving as an optical modulator through a field lens17G. The liquid crystal panel 18G modulates the G light flux in responseto an image signal to form a G-color image. The B light flux transmittedthrough the second dichroic mirror 21 is incident to the liquid crystalpanel 18B serving as an optical modulator through relay lenses 22 and24, reflective mirrors 23 and 25, and a field lens 17B. The liquidcrystal panel 18B modulates the B light flux in response to an imagesignal to form a B-color image.

A cross dichroic prism 19 is a prism for light composition, combineslight fluxes modulated by the liquid crystal panels 18R, 18G, and 18B toform an image light, and causes the image light to travel to aprojection optical system 40.

The projection optical system 40 is a zoom lens for projection, whichprojects an image light modulated by the liquid crystal panels 18G, 18R,and 18B and combined by the cross dichroic prism 19 onto a screen (notshown) on an enlarged scale.

The circuit device 80 includes an image processing unit 81 to which anexternal image signal, such as a video signal, is input, a displaydriving unit 82 which drives the liquid crystal panels 18G, 18R, and 18Bprovided in the optical system section 50 on the basis of an output ofthe image processing unit 81, a lens driving unit 83 which operates adriving mechanism (not shown) provided in the projection optical system40 to adjust a state of the projection optical system 40, and a centralcontrol unit 88 which performs overall control of the operations of thecircuit portions 81, 82, and 83, and the like.

The image processing unit 81 converts the input external image signal toan image signal including the tone of each color or the like. The imageprocessing unit 81 may perform various image processes, such asdistortion correction or color correction, on the external image signal.

The display driving unit 82 can operate the liquid crystal panels 18G,18R, and 18B on the basis of an image signal output from the imageprocessing unit 81, and can form an image corresponding to the imagesignal or an image corresponding to an image signal subjected to theimage process, on the liquid crystal panels 18G, 18R, and 18B.

The lens driving unit 83 operates under the control of the centralcontrol unit 88, and appropriately moves some optical componentsconfiguring the projection optical system 40 along an optical axis OAthrough an actuator AC, thereby it is possible to perform focusing inresponse to magnification change (focusing during magnification change)in projection of an image on a screen by the projection optical system40. Further, the lens driving unit 83 can change a vertical position ofthe image projected on the screen, through adjustment of a tilt at whichthe entire projection optical system 40 moves vertically perpendicularto the optical axis OA.

Hereinafter, the projection optical system 40 of the embodiment will bespecifically described with reference to FIG. 2 and FIG. 3. Theprojection optical system 40 illustrated in FIG. 2 or the like has thesame configuration as the projection optical system 40 of Example 1 tobe described below.

The projection optical system 40 of the embodiment projects an imageformed on a projection-performed surface of the liquid crystal panel 18G(18R or 18B), onto a screen (not shown). A prism PR corresponding to thecross dichroic prism 19 in FIG. 1 is disposed between the projectionoptical system 40 and the liquid crystal panel 18G (18R or 18B).

The projection optical system 40 includes a first optical group 40 awhich is formed of a plurality of lenses and has positive power and asecond optical group 40 b which is configured of one mirror MR with areflective surface having a concave aspherical shape. The first opticalgroup 40 a is formed to have a 1-1st lens group 41 having positivepower, on the reduction side, and a 1-2nd lens group 42 having weakerpositive or negative power, compared to the power of the 1-1st lensgroup 41, on the enlargement side, with the widest air interval BD, as aboundary, of a space formed between included lenses.

The 1-1st lens group 41 has an aperture ST inside thereof and is formedto have a lens group E1 on a reduction side from the aperture ST and alens group E2 on an enlargement side from the aperture ST.

The 1-2nd lens group 42 has, in order from the reduction side, a firstfixed lens group H1 (reduction-side fixed lens group) which is fixedwhen focusing is performed in response to the magnification change,three moving lens groups of an F1 lens group (hereinafter, lens groupF1), an F2 lens group (hereinafter, lens group F2), and an F3 lens group(hereinafter, lens group F3), which individually move in an optical axisdirection when focusing is performed in response to the magnificationchange, a second fixed lens group H2 (enlargement-side fixed lens group)which is fixed when focusing is performed in response to themagnification change. In other words, in the 1-2nd lens group 42, a lensgroup, which is fixed on the outermost enlargement side when focusing isperformed in response to the magnification change, is disposed as thesecond fixed lens group H2 (enlargement-side fixed lens group). As shownin FIG. 2, the second fixed lens group H2 as the enlargement-side fixedlens group is configured of two negative lenses L15 and L16 and the lensL16 disposed on the outermost enlargement side is the aspherical lensmolded using a resin. In addition, the three lens groups F1 to F3(moving lens group) are caused to individually move by the actuator ACin a direction A1 along the optical axis OA when focusing is performedin response to magnification change. Further, the actuator AC can causethe lens groups F1 to F3 to move in various modes by performing of thefocusing during magnification change and, for example, the three groupsmay completely individually move, but may be linked to each other usinga cam mechanism or the like.

Hereinafter, the lenses configuring each lens group will be described inorder from the reduction side. Of the first optical group 40 a, the lensgroup E1 of the 1-1st lens group 41 has eight lenses L1 to L8 and thelens group E2 has two lenses L9 and L10. The first fixed lens group H1as the reduction-side fixed lens group of the 1-2nd lens group 42 hasone lens L11, the lens group F1 as the moving lens group has one lensL12, the lens group F2 has one lens L13, the lens group F3 has one lensL14, and the second fixed lens group H2 as the enlargement-side fixedlens group has two lenses L15 and L16 described above. In other words,the first optical group 40 a is configured to have 16 lenses L1 to L16as a whole.

Of the lenses L1 to L8 configuring the lens group E1, the lens L3 as apositive lens and the lens L4 as a negative lens form a cemented lensand the lens L5 and the lens L6 form a cemented lens. Particularly, thelens L6 is a negative aspherical glass lens and has a concave asphericalsurface on the enlargement side. In other words, the 1-1st lens group 41has at least two sets of cemented lenses of the positive lenses and thenegative lenses on the reduction side from the aperture ST and has atleast one concave aspherical surface on the enlargement side. Further,of the lenses configuring the lens group E1, the lenses other than thelens L6 are spherical glass lenses. In addition, the lenses L1 to L8have a circular shape which is symmetric about the optical axis OA.

For the two lenses L9 and L10 configuring the lens group E2, the lensesL9 is the positive lens and the lens L10 is the negative lens.Particularly, the lens L10 is a negative meniscus lens with the concavesurface facing the enlargement side. In other words, the 1-1st lensgroup 41 is configured to have two lenses of a positive lens with theconvex surface facing the enlargement side and a negative meniscus lenswith the concave surface facing the enlargement side, in this order fromthe reduction side on the enlargement side from the aperture ST.Further, lenses L9 and L10 are spherical glass lenses having a circularshape which is symmetric about the optical axis OA.

The lens L11 configuring the first fixed lens group H1 is a positivemeniscus lens. Further, the lens L11 is the spherical glass lens havinga circular shape which is symmetric about the optical axis OA.

The lens L12 configuring the lens group F1 is a positive biconvex lens.Further, the lens L12 is the spherical glass lens having a circularshape which is symmetric about the optical axis OA.

The lens L13 configuring the lens group F2 is a negative meniscus lens.Further, the lens L13 is the spherical glass lens having a circularshape which is symmetric about the optical axis OA.

The lens L14 configuring the lens group F3 is a lens (aspherical lens)having negative power with both surface subjected to an asphericalsurface process and is a lens (resin lens) molded using a resin.Further, the lens L14 is a circular shape which is symmetric about theoptical axis OA.

Of the lenses L15 and L16 configuring the second fixed lens group H2disposed on the outermost enlargement side of the lens groups, the lensL15 is a negative biconvex lens. Further, the lens L15 is the sphericalglass lens having a circular shape which is symmetric about the opticalaxis OA. The lens L16 is a lens (aspherical lens) which has negativepower with both surface subjected to an aspherical surface process, andis a lens (resin lens) molded using a resin. Further, the lens L16 isnot formed to have a circular shape, but to have a partially notchedshape which is notched on the upper side (side on which an image lightis projected) from a state of a circular shape which is symmetric aboutthe optical axis OA.

The second optical group 40 b is configured of one mirror MR having aconcave aspherical shape and the mirror MR reflects the image lightemitted from the first optical group 40 a, and thereby projects theimage light to a screen.

Further, as described above, in the projection optical system 40, of allof the lenses L1 to L16 configuring the first optical group 40 a, lensesL1 to L15 have a circular shape which is symmetric about the opticalaxis OA and lens L16 has a partially notched shape from a circular shapewhich is symmetric about the optical axis OA. In addition, the mirror MRconfiguring the second optical group 40 b also has a partially notchedshape from a circular shape which is symmetric about the optical axisOA. In other words, elements configuring the first optical group 40 aand the second optical group 40 b all belong to a rotationally symmetricsystem. In addition, as shown in FIG. 1, the reduction side in theprojection optical system 40 is substantially telecentric. For example,as described above, in a case where light fluxes modulated by therespective liquid crystal panels 18R, 18G, and 18B in the cross dichroicprism 19 are combined into an image light, it is possible to herebyeasily absorb variations due to assembly.

In general, a short throw projection optical system including theprojection optical system 40 as above has an abnormally short distanceto a screen. In the projection optical system 40 described above, anobject positioned on a panel surface PI of the liquid crystal panel 18G(18R or 18B) (that is, an image on a panel) in the first optical group40 a, is temporarily formed as an image in front of a mirror of thesecond optical group 40 b, is again formed as an image on a screen byone mirror MR configuring the second optical group 40 b, and therebyshort throw projection is performed in the first optical group 40 a. Inother words, in this case, the first optical group 40 a plays a role offorming a primary image (intermediate image) in front of the mirror MR.In the projection as described above, aberration fluctuation due tofocusing in response to the magnification change is greater than a caseof general projection, and thus it is common not to have a significantlylarge range of magnification change. Accordingly, the primary imageformed by the first optical group 40 a needs to be compatible even in acase where, when an angle of view is abnormally wide and thus projectionmagnification is changed, the aberration fluctuation is likely toincrease. In addition, in the common short throw projection opticalsystem, it is easy to increase contrast reduction due to field curvatureand astigmatism fluctuation which directly influence on imageperformance, and distortion due to movement of a focus group is highlylikely to be also increased more than in a normal lens system.

In comparison, in the present embodiment, as described above, in the1-2nd lens group 42 of the first optical group 40 a, the asphericalresin lens is disposed on the outermost enlargement side and theenlargement-side fixed lens group (second fixed lens group H2) as thefixed group is disposed, the moving lens group, which moves whenfocusing is performed in response to the magnification change, isdisposed on the reduction side from the second fixed lens group H2, andthereby it is possible to perform effective correction so as to suppressthe aberration fluctuation to be small. Even in a case where the secondoptical group 40 b is configured of one mirror MR, it is possible tohereby achieve a good image having small aberration, compared to animage of which the primary image has moderate aberration, and which isfinally projected on the screen through the second optical group 40 b.In other words, in the projector 2 as a short throw type projector, awide range of magnification change is covered and it is possible to bealso applied to an image display element having high resolution.

In the first optical group 40 a, when one aspherical lens is included inthe lenses configuring the 1-2nd lens group 42 as a focusing groupdisposed on the enlargement side, there is a concern that a sufficientrange of magnification change will not be secured by a design. When twoaspherical lenses are included in the 1-2nd lens group 42, it ispossible to widen the range of the magnification change; however, inthis case, in order to sufficiently widen the range of the magnificationchange, the shape of each aspherical lens is highly likely to have ahighly aspherical shape as a significantly different surface shape fromthe spherical shape, surface sensitivity or refractive index sensitivitybecomes high, further eccentricity sensitivity between surfaces alsobecomes high, and there is a high possibility that variation in thefinal lens performance is likely to be increased.

In addition, for the aspherical lens (lens L16) of the 1-2nd lens group42, in order to prevent interference with a light flux reflected fromthe mirror of the second optical group 40 b, not only there is a need tohave an atypical shape such as a partially notched circular shape, butalso, an aspherical resin-molded surface is normally used because thediameter is relatively great such that, in the present embodiment, thelens L16 is also an aspherical resin lens having an atypical shape.However, in general, the aspherical resin-molded surface also has loweraccuracy than the aspherical glass-molded surface, and thus there is aneed to sufficiently reduce sensitivity at the time of design becausethe system is likely to be influenced by variations due to surfaceaccuracy or refractive index as described above.

In comparison, in the present embodiment, even when the 1-2nd lens group42 as the focusing group includes two aspherical lenses (lenses L14 andL16), a negative glass lens (lens L15) is disposed therebetween. In thismanner, the negative power of the aspherical lens is appropriatelydistributed, it is possible to reduce relative sensitivity between theaspherical surface, and it is possible to reduce the aberrationfluctuation even in a wide range of the magnification change.

Further, in the 1-2nd lens group 42 as the focusing group, it is alsopossible to dispose the fixed lens group (second fixed lens group H2) onthe reduction side. In this case, for example, the number of moving lensgroups of the focusing groups is decreased (in Example 2 to be describedbelow, instead of three moving lens groups, configured of two movinglens groups), a frame structure or the like which fixes the lenses issimplified, and it is possible to obtain the entire apparatus at a lowcost.

Further, in the 1-1st lens group 41, if a configuration on the reductionside from the aperture ST has only the spherical lenses, it isconsidered that it is possible to be applied only to brightness havingthe F-number of about 1.8, when applied to a wide range of themagnification change. In comparison, in the present embodiment, theaspherical glass surface (lens L6) is appropriately disposed on thereduction side from the aperture ST, and thereby it is possible toachieve an image having less flare and high contrast even at theF-number of about 1.6. Even when the number of (in the presentembodiment, 16) lenses is substantially the same as an example in therelated art, the numerical aperture on the object side is equal to ormore than 0.3, that is, with brightness having the F-number of about1.6, a range of magnification change of high magnification of 1.5(further, equal to or more than 1.6) is secured, and performance ofsufficient application to the image display element having highresolution is achieved.

EXAMPLE

Hereinafter, a specific example of the projection optical system 40 willbe described. Meanings of specifications common in Examples 1 to 3 inthe following description are defined as follows.

f Focal Length of Entire system

ω Half Angle of View

Na Numerical Aperture

R Curvature Radius

D Axial Top Surface Interval (Lens Thickness Or Lens Interval)

Nd Refractive Index of d Line

Vd Abbe Number of d Line

The aspherical surface is defined by the following polynomial equation(aspherical surface equation).

$z = {\frac{{ch}^{3}}{1 + \sqrt{1 - {\left( {k + 1} \right)c^{3}h^{2}}}} + {A_{2}h^{2}} + {A_{6}h^{6}} + {A_{8}h^{8}} + {A_{10}h^{10}} + {A_{12}h^{12}} + {A_{14}h^{14}}}$

Here,

c: Curvature (1/R)

h: Height From Optical Axis

k: Coefficient Of The Cone Of Aspherical Surface

Ai: Coefficient Of Aspherical Surface In High Order Equation

Example 1

Data of lens surfaces of Example 1 is shown in Table 1. Further, OBJmeans the panel surface PI and STO means the aperture ST. In addition, asurface having “*” after a surface reference number means a surfacehaving aspherical shape.

TABLE 1 f 4.198 ω 72.7 NA 0.313 R D Nd Vd OBJ Infinity 9.400 1 Infinity27.908  1.51633 64.14 2 Infinity 0.000 3 36.468 7.200 1.49700 81.54 4−749.160 0.200 5 43.474 7.800 1.49700 81.54 6 −81.067 0.200 7 40.6869.600 1.51633 64.14 8 −26.047 1.200 1.90366 31.31 9 50.879 0.200 1020.617 6.800 1.51633 64.14 11 −51.334 1.600 1.85400 40.39 *12 47.8281.000 13 27.572 6.400 1.54814 45.78 14 −27.572 0.967 15 −59.872 1.2001.78590 44.20 16 30.662 4.000 STO Infinity 6.661 18 154.078 4.6001.76182 26.52 19 −34.791 4.201 20 69.233 1.400 1.79952 42.22 21 37.52025.172  22 50.763 8.200 1.58913 61.13 23 261.834 variable interval 24257.567 8.000 1.65160 58.55 25 −86.576 variable interval 26 −65.4402.500 1.80518 25.42 27 −202.755 variable interval *28 −83.004 3.5001.53116 56.04 *29 160.357 variable interval 30 −223.590 2.800 1.8051825.42 31 340.269 2.000 *32 −91.539 3.500 1.53116 56.04 *33 136.964116.000  *34 −63.286 variable reflective interval surface 35 Infinity

In Table 1 and the following Tables, an exponent of 10 (for example,1.00×10+18) is described using E (for example, 1.00E+18).

Table 2 shows an aspherical surface coefficient of a lens surface ofExample 1.

TABLE 2 Aspherical Surface Coefficient A04 A06 K A12 A14 A08 A10 1210.0050  2.3741E−05 −2.6694E−08   7.3594E−11 −1.5310E−12   0.0000E+000.0000E−00 28 0.0000 −2.3502E−05 2.2486E−08  9.1144E−13 −4.2273E−15  0.0000E+00 0.0000E+00 29 0.0000 −2.7373E−05 2.7720E−08 −1.2563E−114.2123E−15  0.0000E+00 0.0000E+00 32 3.2860  7.9229E−06 8.1486E−09−1.7567E−11 1.1751E−14 −3.4034E−18 0.0000E+00 33 −1.0000 −4.4919E−061.4099E−08 −1.4126E−11 4.2322E−15  4.7746E−19 −5.0527E−22  34 −1.0000−4.0047E−09 −1.1966E−11  −4.0663E−15 1.0653E−18 −1.5807E−22 8.2232E−27

Table 3 shows values of variable intervals 23, 25, 27, 29, and 34 inTable 2 at the projection magnification of 133 times, the projectionmagnification of 104 times, and the projection magnification of 177times.

TABLE 3 Variable Interval 133x 104x 177x 23 4.692 3.000 6.368 25 4.2914.460 4.135 27 9.610 10.030 9.212 29 9.120 10.225 8.000 34 −600.000−477.420 −784.120

FIG. 4 is a sectional diagram showing the projection optical system ofExample 1. The projection optical system in FIG. 4 corresponds to theprojection optical system 40 of Embodiment 1. Further, the lens L15 orthe mirror MR having a partially notched shape from a circle in FIG. 3or the like is depicted intact without a notch in FIG. 4. In FIG. 4, theprojection optical system performs enlargement projection of an image onthe panel surface PI to the screen at a magnification depending on adistance. In other words, the projection optical system has 16 lenses L1to L16 of the lenses L1 to L8 configuring the lens group E1 of the 1-1stlens group 41, the lenses L9 and L10 configuring the lens group E2thereof, the lens L11 configuring the first fixed lens group H1 of the1-2nd lens group 42, the lens L12 configuring the lens group F1 thereof,the lens L13 configuring the lens group F2 thereof, the lens L14configuring the lens group F3 thereof, and the lenses L15 and L16configuring the second fixed lens group H2, in this order from thereduction side. For example, as in a case where projection onto a wallsurface is changed to projection onto a floor surface, the magnificationchange occurs due to the change of a projection position (change ofprojection distance), and the first and second fixed lens groups H1 andH2 configuring the 1-1st lens group 41 and the 1-2nd lens group 42 arefixed as is when focusing is performed during the magnification change,whereas the lens groups F1 to F3 configuring the 1-2nd lens group 42individually move.

Further, the respective lenses L1 to L16 will be described in detail. Inthe 1-1st lens group 41, the lens L1 as a first lens is a positive lens,the lens L2 as a second lens is a positive lens, the lens L3 as a thirdlens is a positive lens, the lens L4 as a fourth lens is a negativelens, the lens L3 and the lens L4 form a cemented lens, the lens L5 as afifth lens is a positive lens, the lens L6 as a sixth lens is a negativelens having a concave aspherical surface on the enlargement side, thelens L5 and the lens L6 form a cemented lens, the lens L7 as a seventhlens is a positive biconvex lens, the lens L8 as an eighth lens is anegative biconcave lens, the lens L9 as a ninth lens is a positivebiconvex lens, and the lens L10 as the tenth lens is a negative meniscuslens with the concave surface facing the enlargement side. In addition,in the 1-2nd lens group 42, the lens L11 as an eleventh lens is apositive lens, the lens L12 as a twelfth lens is a positive lens, thelens L13 as a thirteenth lens is a negative lens, the lens L14 as afourteenth lens is a negative lens having both surfaces subjected to theaspherical surface process, the lens L15 as a fifteenth lens is anegative biconcave lens, and the lens L16 as a sixteenth lens is anegative lens having both surfaces subjected to the aspherical surfaceprocess. In addition, the second optical group 40 b is configured of onemirror having a concave aspherical surface.

FIG. 5A is a diagram showing aberration (spherical aberration,astigmatism, and distortion) on the reduction side of the projectionoptical system when the projection magnification of 133 times isperformed. FIG. 5B is a diagram showing aberration on the reduction sideof the projection optical system when the projection magnification of104 times is performed. FIG. 5C is a diagram showing aberration on thereduction side of the projection optical system when the projectionmagnification of 177 times is performed. In addition, FIGS. 6A to 6E arediagrams showing lateral aberration of the projection optical system,which correspond to FIG. 5A. FIG. 6A is a diagram showing the lateralaberration in a case of the maximum angle of view and FIGS. 6A to 6E arediagrams showing lateral aberration at five angles of view. Similarly,FIGS. 7A to 7E are diagrams showing lateral aberration of the projectionoptical system, which correspond to FIG. 5B. FIGS. 8A to 8E are diagramsshowing lateral aberration of the projection optical system, whichcorrespond to FIG. 5C.

Example 2

Data of lens surfaces of Example 2 is shown in Table 4. Further, OBJmeans the panel surface PI and STO means the aperture ST. In addition, asurface having “*” after a surface reference number means a surfacehaving aspherical shape.

TABLE 4 f 4.148 ω 72.9 NA 0.313 R D Nd Vd OBJ Infinity 9.400 1 Infinity27.908  1.51633 64.14 2 Infinity 0.000 3 39.984 7.200 1.49700 81.54 4−256.956 0.200 5 36.736 7.800 1.49700 81.54 6 −143.091 0.200 7 30.0599.200 1.48749 70.24 8 −35.819 1.200 1.90366 31.31 9 26.069 0.100 1017.177 7.500 1.48749 70.24 11 −343.444 0.100 *12 122.605 1.600 1.7432049.29 *13 30.892 0.100 *14 18.654 8.000 1.53172 48.84 15 −16.479 1.2001.79952 42.22 16 35.200 4.000 STO Infinity 2.948 18 172.300 4.2001.76182 26.52 19 −28.583 5.164 20 63.999 1.400 1.79952 42.22 21 38.67724.618  22 65.570 8.500 1.58913 61.13 23 −844.941 variable interval 2497.751 9.000 1.69680 55.53 25 −125.923 variable interval 26 −78.5572.500 1.80518 25.42 27 −411.470 8.083 *28 −70.270 3.500 1.53116 56.04*29 316.685 variable interval 30 −78.342 2.800 1.80518 25.42 31 −285.3602.000 *32 −80.937 3.500 1.53116 56.04 *33 118.799 118.535  *34 −63.897variable reflective interval surface 35 Infinity

Table 5 shows an aspherical surface coefficient of a lens surface ofExample 2.

TABLE 5 Aspherical Surface Coefficient A04 A06 K A12 A14 A08 A10 1241.7552 −3.1150E−05 4.7440E−07 −2.7695E−09 1.1259E−11 −1.9427E−140.0000E+00 13 5.0559 −1.7738E−05 4.6868E−07 −3.0405E−09 1.1757E−11−2.5631E−14 0.0000E+00 28 0.0000 −1.8992E−05 2.1986E−08 −3.8853E−12−4.0246E−15   0.0000E+00 0.0000E+00 29 0.0000 −2.2802E−05 2.2365E−08−7.5936E−12 0.0000E+00  0.0000E+00 0.0000E+00 32 3.2860  2.4060E−063.9245E−09  4.4949E−12 −1.3592E−14   7.5488E−18 0.0000E+00 33 −1.0000−1.0274E−05 1.6113E−08 −1.7475E−11 1.4398E−14 −1.0369E−17 3.8391E−21 34−1.0000  1.5584E−08 −2.7437E−11   2.7366E−15 −4.9253E−19   3.8224E−23−2.0614E−27 

Table 6 shows values of variable intervals 23, 25, 29, and 34 in Table 5at the projection magnification of 135 times, the projectionmagnification of 106 times, and the projection magnification of 179times.

TABLE 6 variable interval 133x 104x 177x 23 2.579 1.500 3.678 25 6.8136.782 6.866 29 12.151 13.261 11.000 34 −600.000 −476.470 −785.931

FIG. 9 is a sectional diagram showing the projection optical system ofExample 2. Further, the lens L16 or the mirror MR having a partiallynotched shape from a circle in an actual optical system is depictedintact without a notch in FIG. 9. In FIG. 9, the projection opticalsystem performs enlargement projection of an image on the panel surfacePI to the screen at a magnification depending on a distance. In otherwords, the projection optical system has 16 lenses L1 to L16 of thelenses L1 to L8 configuring the lens group E1 of the 1-1st lens group41, the lenses L9 and L10 configuring the lens group E2 thereof, thelens L11 configuring the first fixed lens group H1 of the 1-2nd lensgroup 42, the lens L12 configuring the lens group F1 thereof, the lensesL13 and L14 configuring the lens group F2 thereof, and the lenses L15and L16 configuring the second fixed lens group H2, in this order fromthe reduction side. For example, as in a case where projection onto awall surface is changed to projection onto a floor surface, themagnification change occurs due to the change of a projection position(change of projection distance), and the first and second fixed lensgroups H1 and H2 configuring the 1-1st lens group 41 and the 1-2nd lensgroup 42 are fixed as is when focusing is performed during themagnification change, whereas the lens groups F1 and F2 configuring the1-2nd lens group 42 individually move.

As above, in Example 2, the first optical group 40 a is configured tohave 16 lenses from the lens L1 (first lens) to the lens L16 (sixteenthlens) numbered from the reduction side, and the first optical group 40 acan be divided into the 1-1st lens group 41 having positive power, onthe reduction side, and the 1-2nd lens group 42 having weaker positiveor negative power, compared to the power of the 1-1st lens group 41, onthe enlargement side, with the widest air interval BD as a boundary.

More specifically, the 1-1st lens group 41 is configured to include thelens group E1 having the positive lens L1, the positive lens L2, thecemented lens of the positive lens L3 and the negative lens L4, thepositive lens L5, the negative lens L6 having both surfaces subjected tothe aspherical surface process, the cemented lens of the positive lensL7 and the negative lens L8, the aperture ST, and the lens group E2having the positive biconvex lens L9, and the negative meniscus lens L10with the concave surface facing the enlargement side, in this order fromthe reduction side. In other words, a total of ten lenses in lens groupsE1 and E2 are sequentially arranged.

The 1-2nd lens group 42 is configured to include the first fixed lensgroup H1 having the positive lens L11, the lens group F1 (F1 lens group)having the positive lens L12, the lens group F2 (F2 lens group) havingthe negative lens L13 and the negative lens L14 having both surfacessubjected to the aspherical surface process, and the second fixed lensgroup H2 having the negative meniscus lens L15 with the convex surfacefacing the enlargement side and the negative lens L16 having bothsurfaces subjected to an aspherical surface process, in this order fromthe reduction side. In other words, a total of six lenses in the fixedlens groups H1 and H2 and the lens groups F1 and F2 are sequentiallydisposed. The lens L14 and the lens L16 are lenses molded using a resin.In addition, the 1-2nd lens group 42 performs focusing by causing thetwo lens groups F1 and F2 to individually move, when the projectiondistance is changed during the magnification change.

The second optical group 40 b is configured of one mirror having aconcave aspherical surface.

FIG. 10A is a diagram showing aberration (spherical aberration,astigmatism, and distortion) on the reduction side of the projectionoptical system when the projection magnification of 135 times isperformed. FIG. 10B is a diagram showing aberration on the reductionside of the projection optical system when the projection magnificationof 106 times is performed. FIG. 10C is a diagram showing aberration onthe reduction side of the projection optical system when the projectionmagnification of 179 times (170 times) is performed. In addition, FIGS.11A to 11E are diagrams showing lateral aberration of the projectionoptical system, which correspond to FIG. 10A. FIG. 11A is a diagramshowing the lateral aberration in a case of the maximum angle of viewand FIGS. 11A to 11E are diagrams showing lateral aberration at fiveangles of view. Similarly, FIGS. 12A to 12E are diagrams showing lateralaberration of the projection optical system, which correspond to FIG.10B. FIGS. 13A to 13E are diagrams showing lateral aberration of theprojection optical system, which correspond to FIG. 10C.

Example 3

Data of lens surfaces of Example 3 is shown in Table 7. Further, OBJmeans the panel surface PI and STO means the aperture ST. In addition, asurface having “*” after a surface reference number means a surfacehaving aspherical shape.

TABLE 7 f 4.154 ω 73.0 NA 0.313 R D Nd Vd OBJ Infinity 9.400 1 Infinity27.908  1.51633 64.14 2 Infinity 0.000 3 40.191 8.456 1.49700 81.54 4−119.236 0.200 5 40.835 7.800 1.49700 81.54 6 −96.666 0.200 7 44.5919.600 1.51633 64.14 8 −26.059 1.200 1.90366 31.31 9 42.427 0.200 1019.505 6.800 1.51633 64.14 11 −120.030 1.600 1.85400 40.39 *12 39.8951.000 13 26.667 6.400 1.54814 45.78 14 −27.294 0.986 15 −51.302 1.2001.78590 44.20 16 31.966 4.000 STO Infinity 5.905 18 139.580 4.6001.76182 26.52 19 −34.639 3.798 20 66.572 1.400 1.79952 42.22 21 35.700variable interval 22 54.749 8.765 1.58913 61.13 23 −1483.212 variableinterval 24 460.597 8.000 1.65160 58.55 25 −75.696 5.453 26 −53.2122.500 1.80518 25.42 27 −119.728 variable interval *28 −58.176 3.5001.53116 56.04 *29 128.586 variable interval 30 −125.246 2.800 1.8051825.42 31 1912.349 2.000 *32 −78.179 3.500 1.53116 56.04 *33 −3823.231113.625  *34 −61.466 variable reflective interval surface 35 Infinity

Table 8 shows an aspherical surface coefficient of a lens surface ofExample 3.

TABLE 8 Aspherical Surface Coefficient A04 A06 K A12 A14 A08 A10 126.4461 2.2175E−05 −1.6365E−08   7.5210E−11 −1.5183E−12  0.0000E+000.0000E+00 28 0.0000 −1.2680E−05  1.8029E−08 −1.1193E−11 4.8015E−150.0000E+00 0.0000E+00 29 0.0000 −2.2927E−05  2.2016E−08 −1.5103E−116.2559E−15 0.0000E+00 0.0000E+00 32 3.2860 9.5153E−06 1.1223E−08−2.0865E−11 1.1925E−14 −3.0782E−18  0.0000E+00 33 −1.0000 1.5255E−061.0843E−08 −8.3444E−12 −1.4840E−15  8.2465E−19 4.8363E−22 34 −1.00002.7182E−08 −1.3766E−11  −5.3481E−15 1.4526E−18 −1.9708E−22  9.1483E−27

Table 9 shows values of variable intervals 21, 23, 27, 29, and 34 inTable 8 at the projection magnification of 135 times, the projectionmagnification of 106 times, and the projection magnification of 223times.

TABLE 9 Variable Interval 133x 104x 177x 21 24.532 24.415 25.047 233.955 2.000 6.769 27 9.142 10.254 7.714 29 9.847 10.861 8.000 34−600.000 −475.698 −974.783

FIG. 14 is a sectional diagram showing the projection optical system ofExample 3. Further, the lens L16 or the mirror MR having a partiallynotched shape from a circle in an actual optical system is depictedintact without a notch in FIG. 14. In FIG. 14, the projection opticalsystem performs enlargement projection of an image on the panel surfacePI to the screen at a magnification depending on a distance. In otherwords, the projection optical system has 16 lenses L1 to L16 of thelenses L1 to L8 configuring the lens group E1 of the 1-1st lens group41, the lenses L9 and L10 configuring the lens group E2 thereof, thelens L11 configuring the lens group F1 of the 1-2nd lens group 42, thelenses L12 and L13 configuring the lens group F2 thereof, the lens L14configuring the lens group F3 thereof, and the lenses L15 and L16configuring the second fixed lens group H2, in this order from thereduction side. Further in the present embodiment, the fixed lens groupdoes not exist on the reduction side in the 1-2nd lens group 42. Inother words, the lens corresponding to the first fixed lens group 1 doesnot exist. For example, as in a case where projection onto a wallsurface is changed to projection onto a floor surface, the magnificationchange occurs due to the change of a projection posit ion (change ofprojection distance), and the 1-1st lens group 41 and the second fixedlens group H2 configuring the 1-2nd lens group 42 are fixed as is whenfocusing is performed during the magnification change, whereas the lensgroups F1 to F3 configuring the 1-2nd lens group 42 individually move.

As above, in Example 3, the first optical group 40 a is configured tohave 16 lenses from the lens L1 (first lens) to the lens L16 (sixteenthlens) numbered from the reduction side, and the first optical group 40 acan be divided into the 1-1st lens group 41 having positive power, onthe reduction side, and the 1-2nd lens group 42 having weaker positiveor negative power, compared to the power of the 1-1st lens group 41, onthe enlargement side, with the widest air interval BD as a boundary.

More specifically, the 1-1st lens group 41 is configured to include thelens group E1 having the positive lens L1, the positive lens L2, thecemented lens of the positive lens L3 and the negative lens L4, thecemented lens of the positive lens L5 and the negative lens L6 subjectedto the concave aspherical surface process on the enlargement side, thepositive biconvex lens L7, and the negative biconcave lens L8, theaperture ST, and the lens group E2 having the positive biconvex lens L9,and the negative meniscus lens L10 with the concave surface facing theenlargement side, in this order from the reduction side. In other words,a total of ten lenses in lens groups E1 and E2 are sequentiallyarranged.

The 1-2nd lens group 42 is configured to include the lens group F1 (F1lens group) having the positive lens L11, the lens group F2 (F2 lensgroup) having the positive lens L12 and the negative lens L13, the lensgroup F3 (F3 lens group) having the negative lens L14 having bothsurfaces subjected to the aspherical surface process, and the fixed lensgroup H2 having the negative biconcave lens L15 and the negative lensL16 having both surfaces subjected to an aspherical surface process, inthis order from the reduction side. In other words, a total of sixlenses in the lens groups F1 to F3 and in the fixed lens group H2 aresequentially disposed. The lens L14 and the lens L16 are lenses moldedusing a resin. In addition, the 1-2nd lens group 42 performs focusing bycausing the three lens groups F1 to F3 to individually move, when theprojection distance is changed during the magnification change.

The second optical group 40 b is configured of one mirror having aconcave aspherical surface.

FIG. 15A is a diagram showing aberration (spherical aberration,astigmatism, and distortion) on the reduction side of the projectionoptical system when the projection magnification of 135 times isperformed. FIG. 15B is a diagram showing aberration on the reductionside of the projection optical system when the projection magnificationof 106 times is performed. FIG. 15C is a diagram showing aberration onthe reduction side of the projection optical system when the projectionmagnification of 223 times is performed. In addition, FIGS. 16A to 16Eare diagrams showing lateral aberration of the projection opticalsystem, which correspond to FIG. 15A. FIG. 16A is a diagram showing thelateral aberration in a case of the maximum angle of view and FIGS. 16Ato 16E are diagrams showing lateral aberration at five angles of view.Similarly, FIGS. 17A to 17E are diagrams showing lateral aberration ofthe projection optical system, which correspond to FIG. 15B. FIGS. 18Ato 18E are diagrams showing lateral aberration of the projection opticalsystem, which correspond to FIG. 15C.

SUMMARY OF EXAMPLES

In any one of Examples, a simple configuration, in which the lens on theoutermost enlargement side is one aspherical resin lens, is employedwhile a wide angle of view is equal to or greater than a half angle ofview of 70° at a wide angle end.

The invention is not limited to the embodiments or examples describedabove and can be performed in various aspects within a range withoutdeparting from the gist thereof.

In addition, in the respective Examples, one or more lenses havingsubstantially no power may be added before and after or between thelenses configuring each lens group.

In addition, a target of enlargement projection by the projectionoptical system 40 is not limited to the liquid crystal panels 18G, 18R,and 18B, but it is possible for the projection optical system 40 toperform enlargement projection of an image formed by various light fluxmodulating elements such as a digital micromirror device, in which amicromirror functions as a pixel.

The entire disclosure of Japanese Patent Application No. 2015-029305,filed Feb. 18, 2015 is expressly incorporated by reference herein.

What is claimed is:
 1. A projection optical system comprising: in orderfrom a reduction side, a first optical group which is formed of aplurality of lenses and has positive power; and a second optical groupwhich has one reflective surface having a concave aspherical shape,wherein the first optical group is formed to include a 1-1st lens grouphaving positive power, on the reduction side, and a 1-2nd lens grouphaving weaker positive or negative power, compared to the power of the1-1st lens group, on the enlargement side, with the widest air intervalas a boundary, and wherein the 1-2nd lens group includes anenlargement-side fixed lens group which is disposed on the outermostenlargement side, is fixed when focusing is performed in response to themagnification change, and is configured to include a plurality of lenseshaving at least one aspherical surface, and at least one moving lensgroup which moves in the optical axis direction when focusing isperformed in response to the magnification change.
 2. The projectionoptical system according to claim 1, wherein, in the 1-2nd lens group,the enlargement-side fixed lens group is configured to include twonegative lenses and an aspherical lens molded using a resin is disposedon the enlargement side.
 3. The projection optical system according toclaim 1, wherein the 1-2nd lens group has, as the moving lens group, aplurality of lens groups which individually move when focusing isperformed in response to the magnification change.
 4. The projectionoptical system according to claim 1, wherein the 1-1st lens group isconfigured to have an aperture therein and two lenses of a positive lenswith a convex surface facing the enlargement side and a negativemeniscus lens with the concave surface facing the enlargement side, inthis order from the reduction side, on the enlargement side from theaperture.
 5. The projection optical system according to claim 1, whereinthe 1-1st lens group includes an aperture therein, includes at least twosets of cemented lenses of positive lenses and negative lenses disposedon the reduction side from the aperture, and has at least a concaveaspherical surface on the enlargement side.
 6. The projection opticalsystem according to claim 1, wherein the numerical aperture on theobject side is equal to or more than 0.3.
 7. The projection opticalsystem according to claim 1, wherein the reduction side is substantiallytelecentric.
 8. The projection optical system according to claim 1,wherein elements configuring the first optical group and the secondoptical group all have a rotationally symmetric system.
 9. Theprojection optical system according to claim 1, wherein a range ofmagnification change is equal to or greater than 1.5 times.